john martin is a colleague of professor graham's at the universy of florida water institute. his team studieshe healthof t, sampling and testing its water for signs of pollution. because of sandy soils and the soluble limestone-bedrock geology in this part of florida, rivers here run above ground and then flow underground through sinkholes. above ground, water can be sampled directly. but underground, the water fills and moves through the porous rock aquifer. this water can be accessed through a series of wells. the aquifer water here, the water that's contained in the rocks in the very small, microscopic, pore spaces within the rock, is what's utilized for drinking water and, actually, allater, so agriculture-irrigation water, bottling water, any kind of water usage is almost all from ground water. narrator: by carefully measuring the depth of ground water, main's team can calculate how much is being used. 17.29. they also record the water's chemical composition to determine nutrient levels that could adversely affect the health of the water. okay, we're ready to sample. nar